Electrical power distribution systems with a bypass unit that couples to a load and electrically engages one of two alternate units for powering the load and related methods

ABSTRACT

Electrical power distribution devices with a bypass unit that electrically engages one of two alternate units for powering a load while electrically isolating the other using a six pole power transfer switch and mechanical and electrical interlocks to allow a technician to access one of the alternate units when de-energized and in position while the other of the alternate units is energized and powering the load.

RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. ProvisionalApplication Ser. No. 62/867,980, filed Jun. 28, 2019, the content ofwhich is hereby incorporated by reference as if recited in full herein.

FIELD OF THE INVENTION

The present invention relates to electrical power distribution systemsand is particularly suitable for motor control centers.

BACKGROUND OF THE INVENTION

In general, electrical power distribution systems distribute electricalpower from power sources, such as private or public power grids, todifferent loads, such as motors. As a specific example, motor controlcenters (MCC) distribute electrical power to and control motors in acentral location. MCCs can include structures, cabinets or enclosurescontaining a common power bus and multiple, typically modular, bucketassemblies or units, which generally contain a motor starter of varioustypes, a circuit breaker or fuse(s) and a power disconnect. See, e.g.,U.S. Pat. No. 4,024,441, the contents of which are hereby incorporatedby reference as if recited in full herein. Eaton Corporation hasrecently introduced a MCC product line with compact bucket assembliesthat conveniently plug into a slot, compartment or space in an MCCstructure. The product is sold under the product name, Freedom 2100 MCC.See also, U.S. Pat. No. 8,934,218, the contents of which are herebyincorporated by reference as if recited in full herein.

SUMMARY OF EMBODIMENTS OF THE INVENTION

Embodiments of the invention are directed to enclosed bypass units thatcan connect to separate primary and secondary units with motor starters,allowing for one to power a load at any one time through the bypass unitwhile electrically isolating the other thereby providing redundantpowering options which can electrically isolate the primary andsecondary units from a load and/or line side bus and each other.

Embodiments of the invention are directed to electrical powerdistribution systems that include: a power bus; a bypass unit with apower transfer switch coupled to a load; a first unit with a firstdisconnect switch configured to selectively couple the power bus to thepower transfer switch; and a second unit with a second disconnect switchconfigured to selectively couple the power bus to the power transferswitch. The power transfer switch of the bypass unit is configured toselectively couple the first unit to the load or the second unit to theload. When the power transfer switch couples the first unit to the load,the first disconnect switch is closed while the second disconnect switchis open to electrically isolate the second unit from the load and thefirst unit. When the power transfer switch couples the second unit tothe load, the second disconnect switch is closed while the firstdisconnect switch is open to electrically isolate the first unit fromthe load and the second unit.

The first and second units can each further include a housing and apower disconnect assembly with extendable/retractable power stabs thatindependently move relative to the housing to connect to and disconnectfrom the power bus. The extendable/retractable power stabs of only oneof the first unit or the second unit can be permitted to be connected tothe power bus at any one time.

The bypass unit can include a housing with a front wall, side walls anda closed rear wall and can be devoid of power stabs. The bypass unit canbe configured so that it does not directly connect to the power bus.

Each of the bypass unit, the first unit and the second unit can includea separate housing that is independently insertable and removable from arespective compartment in at least one structure of the electrical powerdistribution system.

The electrical power distribution system can also include at least onestructure with defined spaced-apart internal compartments that hold thebypass unit, the first unit and the second unit in different ones of thedefined spaced-apart internal compartments. The first unit can have afirst front door with a first disconnect operator handle operablycoupled to the first disconnect switch. The second unit can have asecond front door with a second disconnect operator handle operablycoupled to the second disconnect switch. The electrical powerdistribution system can further include interlocks that (a) prevent thefirst door from opening when either the first disconnect switch isclosed or the first unit is coupled to the load and (b) prevent thesecond door from opening when either the second disconnect switch isclosed or the second unit is coupled to the load.

The bypass unit and the first and second units can be configured to beinsertable into and removable from spaced-apart compartments of astructure.

The first and second disconnect switches can be circuit breakers, andthe first and second units can be operatively connected and configuredto cause a first one of either the first disconnect switch or the seconddisconnect switch to trip to an open state when a second one of thefirst disconnect switch or the second disconnect switch is closed toallow conduction whereby only a single one of the first or seconddisconnect switch is in an on state at any one time.

The electrical power distribution system can be a motor control center(MCC).

The first disconnect switch and the second disconnect switch can eachinclude or be a circuit breaker.

The first unit can have a first motor starter and the second unit canhave a second motor starter.

The first unit and the second unit can have a motor starter and beconfigured as one of options A-L:

Option first unit second unit A VFD unit VFD unit B Soft Starter SoftStarter (Reduced Voltage starter) unit (Reduced Voltage starter) unit CNEMA Starter unit NEMA Starter unit D IEC Starter unit IEC Starter unitE VFD unit Soft Starter (Reduced Voltage starter) unit F Soft StarterNEMA Starter unit (Reduced Voltage starter) unit G NEMA Starter unit IECStarter unit H VFD unit NEMA Starter unit I Soft Starter IEC Starterunit (Reduced Voltage starter) unit J VFD unit IEC Starter unit K FeederBreaker Feeder Breaker L Feeder Fused Feeder Fused Disconnect SwitchDisconnect Switch

The power transfer switch can include a six-pole isolating switch. Thesix-pole isolating switch can have a first set of three switch contactscoupled to the first unit and a second set of three switch contactscoupled to the second unit to thereby allow the six-pole isolatingswitch to selectively couple the first unit or the second unit to theload.

The bypass unit can further include a first conductor coupled to thefirst set of switch contacts, a second conductor coupled to the secondset of switch contacts, and a third conductor configured to couple tothe load, the first conductor extending from the bypass unit a distancesufficient to couple to the first unit, the second conductor extendingfrom the bypass unit a distance sufficient to couple to the second unit,and the third conductor having a length sufficient to couple to theload.

The first and second conductors can extend from the bypass unit througha wire way to connect to the respective first and second units.

The electrical power distribution system can be a motor control center(MCC). The first and second units can each further include a powerdisconnect assembly with extendable/retractable power stabs that moverelative to a rear of the first and second units, respectively, toconnect and disconnect from the power bus. Only a single one of thefirst and second units extend respective power stabs to connect to thepower bus at any one time. The first unit and the second unit eachcomprise a lock that, when deployed, physically (a) locks the powerdisconnect assembly in at least one defined position associated with oneor both (i) a retracted position associated with an electricallyisolated state of the respective unit or (ii) an extended positionassociated with engagement with the power bus and an electrically activestate, and/or (b) locks a laterally movable slide from allowing accessto an aperture that allows a crank to change a position of the powerstabs.

The electrical power distribution system can further include at leastone interlock that is configured to allow a user to open or slidablyremove one of the first unit or the second unit from the MCC only when arespective unit is in the electrically isolated state while allowinganother one of the first or the second unit to be energized and powerthe load through the bypass unit.

Each of the first and second units can be slidably and releasably heldin defined separate compartments of a structure of the electrical powerdistribution system and each is serially interchangeable with adifferent corresponding unit having a common size and shape housingthereby allowing modular repair and replacement. The bypass unit can beheld in a housing with a closed front door and can have a height that isin a range of about 6-12 inches.

The bypass unit, the first unit and the second unit can be held inseparate housings. The bypass unit, the first unit and the second unitcan be configured to power a load with horsepower in a range of about ¼horsepower to 200 horsepower. The bypass unit can have a closed frontdoor with a front operating switch handle coupled to the isolationswitch.

The power transfer switch of the bypass unit can include a six-poleisolation switch defining a main switch body and at least one auxiliaryswitch attached thereto. The at least one auxiliary switch can beconfigured to transmit and/or receive control signals to/from at leastone of the first or second units.

The first disconnect switch can include a first circuit breaker and thesecond disconnect switch can include a second circuit breaker. The firstand second circuit breakers can be electrically interlocked, such thatonly one of the first and second circuit breakers can be closed at anyone time.

The units can be operatively connected and configured to cause a firstone of either the first circuit breaker or the second circuit breaker totrip to an open state when a second one of the first circuit breaker orthe second circuit breaker is closed to allow only a single one of thefirst or second circuit breaker to be in an on state at any one time.

The first disconnect switch can include a first circuit breaker and thesecond disconnect switch includes a second circuit breaker. The firstand second circuit breakers and the power transfer switch can beelectrically interlocked, such that, when the power transfer switchcouples one of the first and second units to the load, only theassociated first or second circuit breaker can be closed.

The power transfer switch can include at least one auxiliary switchcoupled to the circuit breakers that is configured to transmit a tripsignal to the circuit breaker of the first disconnect switch when thepower transfer switch couples the second unit to the load.

Other embodiments are directed to a bypass unit for an electrical powerdistribution system, such as a motor control center, including astructure defining a plurality of compartments having first and secondunits installed therein. The bypass unit includes a housing configuredto insertable into and removable from a compartment and a bypass circuitincluding a power transfer switch in the housing. The power transferswitch includes a six-pole isolation switch configured to selectivelycouple the first unit to a load and the second unit to the load. Thesix-pole isolation switch includes a first set of three switch contactsof the six-pole switch configured to couple to the first unit and asecond set of three switch contacts configured to couple to the secondunit.

The bypass unit can further include a first conductor electricallycoupled to the first set of switch contacts and that extends out of thehousing and is configured to electrically couple to the first unit and asecond conductor that is electrically coupled to the second set ofswitch contacts and that extends out of the housing and is configured toelectrically couple to the second unit. The first unit and/or the secondunit can include a motor starter.

The housing can have a height in a range of about 6-12 inches.Optionally, the bypass unit further includes an operator handle coupledto the six-pole isolation switch and having a first ON positionassociated with the first set of three switch contacts and a second ONposition associated with the second set of three switch contacts

The power transfer switch can be configured to power a load from a powerbus to the load using a single one of the first unit or the second unitat any one time during normal operation and only when a disconnectswitch of another one of the first unit or the second unit is in an offstate associated with non-conduction.

The housing can be rectangular and configured to be slidably andreleasably held in the compartment.

The bypass unit can further include at least one auxiliary switchattached to the six-pole isolation switch, wherein the at least oneauxiliary switch is configured to transmit and/or receive controlsignals to/from at least one of the first or second units.

Embodiments of the invention are directed to electrical powerdistribution systems that include: a bypass unit with a power transferswitch configured to electrically couple to a load; a first unit thatincludes a first disconnect switch electrically coupled to the powertransfer switch; and a second unit that includes a second disconnectswitch electrically coupled to the power transfer switch. At any onepoint in time during normal operation, the power transfer switch of thebypass unit is configured to electrically connect a power bus to theload using only one of the first unit or the second unit. When the powertransfer switch electrically connects the first unit to the load, thefirst disconnect switch is electrically on and allows conduction in anelectrically active (energized) state while the second disconnect switchis electrically off and in an electrically inactive (non-energized)state with the second unit electrically isolated from the load and thefirst unit. When the power transfer switch electrically connects thesecond unit to the load, the second disconnect switch is electrically onand allows conduction in an electrically active (energized) state whilethe first disconnect switch is electrically off and in an electricallyinactive (non-energized) state with the first unit electrically isolatedfrom the load and the second unit.

The first and second units can each further include a power disconnectassembly with extendable/retractable power stabs that move relative to arear of the first and second units, respectively, to connect anddisconnect from the power bus, and only a single one of the first andsecond units have power stabs in an extended state to connect to thepower bus at any one time.

The bypass unit can include an enclosure with a front wall, side wallsand a closed rear wall and can be devoid of power stabs and does notdirectly connect to the power bus.

Each of the bypass unit, the first unit and the second unit can be heldin separate housings and can be independently slidably removable from arespective compartment in at least one structure of the electrical powerdistribution system.

Other embodiments are directed to methods of assembling an electricalpower distribution system. The methods include; providing a bypass unitin a housing comprising a power transfer switch configured to seriallyelectrically couple to only two units defined by first and secondseparate units held in separate respective housings to a load, each ofthe two units to thereby provide a redundant, back-up drive capacity;and selecting only two units as the first and second units to connect tothe bypass unit from one of options A-L:

Option first unit second unit A VFD unit VFD unit B Soft Starter SoftStarter (Reduced Voltage starter) unit (Reduced Voltage starter) unit CNEMA Starter unit NEMA Starter unit D IEC Starter unit IEC Starter unitE VFD unit Soft Starter (Reduced Voltage starter) unit F Soft StarterNEMA Starter unit (Reduced Voltage starter) unit G NEMA Starter unit IECStarter unit H VFD unit NEMA Starter unit I Soft Starter IEC Starterunit (Reduced Voltage starter) unit J VFD unit IEC Starter unit K FeederBreaker Feeder Breaker L Feeder Fused Disconnect Feeder Fused DisconnectSwitch Switch

The first and second units can each comprise a power disconnect assemblyhaving extendable/retractable power stabs.

The methods can further include: slidably inserting the bypass unit andthe selected first and second units into compartments of a structure ofthe electrical power distribution system; and electrically connectingthe power transfer switch of the bypass unit to the selected first andsecond units during, before or after the inserting.

The electrical power distribution system can be a motor control center.

The selected first and second units and the bypass unit can each have adedicated, respective front door. The bypass unit can have a closed rearpanel. A side wall of the bypass unit can have a plurality of conductorsextending outward therefrom including a conductor that couples to aload, and first and second conductors that couple to the selected firstand second units.

The power transfer switch of the bypass unit can include a six-poleisolation switch and at least one auxiliary switch attached thereto. Theat least one auxiliary switch can be configured to transmit and/orreceive control signals to/from at least one of the first or secondunits.

The power transfer switch can include a six-pole isolating switchconfigured to electrically couple to a load, and with a first set ofthree switch contacts coupled only to the first unit while a second setof three switch contacts that are different from the first set of threeswitch contacts and are coupled only to the second unit to therebyserially couple the load to the first unit and the second unit via thebypass unit.

The bypass unit can further include at least one auxiliary switchattached to the six-pole isolation switch. The at least one auxiliaryswitch can be configured to transmit and/or receive control signalsto/from at least one of the first or second units.

Further features, advantages and details of the present invention willbe appreciated by those of ordinary skill in the art from a reading ofthe figures and the detailed description that follow, such descriptionbeing merely illustrative of the present invention.

It is noted that aspects of the invention described with respect to oneembodiment, may be incorporated in a different embodiment although notspecifically described relative thereto. That is, all embodiments and/orfeatures of any embodiment can be combined in any way and/orcombination. Applicant reserves the right to change any originally filedclaim or file any new claim accordingly, including the right to be ableto amend any originally filed claim to depend from and/or incorporateany feature of any other claim although not originally claimed in thatmanner. These and other objects and/or aspects of the present inventionare explained in detail in the specification set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a box diagram of an example electrical power distributionsystem according to embodiments of the present invention.

FIG. 2A is a schematic of an exemplary bypass unit according toembodiments of the present invention.

FIG. 2B is a front, side perspective view of the bypass unit shown inFIG. 2A according to embodiments of the present invention.

FIG. 2C is a rear, side perspective view of the bypass unit shown inFIG. 2A according to embodiments of the present invention.

FIGS. 3A and 3B are box diagrams of electrical power distributionsystems according to embodiments of the present invention.

FIGS. 4-6 are schematic illustrations of electrical power distributionsystems according to embodiments of the present invention.

FIG. 7A is an enlarged front view of a transfer switch and deadfrontswitch handle suitable for the bypass unit shown in FIGS. 1 and 2Aaccording to embodiments of the present invention.

FIG. 7B is a schematic illustration of an electrical power distributionsystem according to embodiments of the present invention.

FIG. 8 is a partial front side perspective view of a motor controlcenter (MCC) according to embodiments of the present invention.

FIG. 9 is a top, side perspective view of an example unit with powerstabs according to embodiments of the present invention.

FIG. 10 is a bottom view of the example unit shown in FIG. 9 accordingto embodiments of the present invention.

FIG. 11 is a table of actions/conditions an electrical interlockingsystem for electrical power distribution systems according toembodiments of the present invention.

FIG. 12 is a table of actions/conditions for a mechanical interlockingsystem according to embodiments of the present invention.

FIG. 13A is a partial front view of a front panel segment of an exampleunit with a keyed interlock according to embodiments of the presentinvention.

FIG. 13B is a top view of the device shown in FIG. 13A.

FIG. 14A is an enlarged view of the keyed interlock shown in FIG. 13A.

FIG. 14B is an enlarged view of a mechanically locked slide of a unit ofthe MCC shown in FIG. 8.

FIGS. 15A and 15B is a flow chart of actions that can be carried out topower a load according to embodiments of the present invention.

FIG. 16 is a flow chart of an example build process allowing for enduser builds from a defined set of modular unit options according toembodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which illustrativeembodiments of the invention are shown. Like numbers refer to likeelements and different embodiments of like elements can be designatedusing a different number of superscript indicator apostrophes (e.g., 10,10′, 10″, 10′″).

In the drawings, the relative sizes of regions or features may beexaggerated for clarity. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother region, layer or section. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the present invention.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device or system in use or operation in addition tothe orientation depicted in the figures. For example, if the device orsystem in the figures is turned over, elements described as “below” or“beneath” other elements or features would then be oriented “above” theother elements or features. Thus, the exemplary term “below” canencompass both an orientation of above and below. The device or systemmay be otherwise oriented (rotated 90° or at other orientations) and thespatially relative descriptors used herein interpreted accordingly.

The term “about”, when used with a number, refers to numbers in a rangeof +/−20% of the noted value(s).

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless expressly stated otherwise. Itwill be further understood that the terms “includes,” “comprises,”“including” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. It will be understood thatwhen an element is referred to as being “connected” or “coupled” toanother element, it can be directly connected or coupled to the otherelement or intervening elements may be present. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of this specification andthe relevant art and will not be interpreted in an idealized or overlyformal sense unless expressly so defined herein.

The terms “operating mechanism” and “operator mechanism” are usedinterchangeably and refer to an assembly that is a primary disconnectfor a unit and typically has a manually operative lever for opening andclosing separable contacts in a circuit breaker and/or for turning powerON and OFF using a disconnect switch associated with a fuse (e.g., afused disconnect). When a disconnect switch of the operating mechanism(e.g., circuit breaker) is ON (with contacts closed) and connected to apower bus, the unit is energized.

The terms “bucket assembly”, “bucket”, “control unit,” and “unit” areused interchangeably and refer to a housing (typically a protectivemetal shell) that contains a disconnect switch, such as an isolationswitch (for a bypass unit), a fused disconnect switch, or a circuitbreaker (which can be manually operated by an operator mechanism) forcontrolling energization/de-energization of the power circuit in theunit. A unit can also include other components such as a powertransformer, PLCs (programmable logic controllers), position sensors andthe like.

The unit can be a motor starter unit, a feeder unit, a unit with atransfer switch or any other unit type. The term “motor starter” is usedherein to refer to any starter type. The motor starter can be, forexample, a variable frequency drive (VFD) (also known as a variablespeed drive), a soft starter (reduced voltage starter), a NEMA starter(NEMA contactor and overload relay, or an IEC starter (IEC contactor andoverload relay). The unit can comprise a feeder such as a feeder with acircuit breaker (“feeder breaker”) or a feeder with a disconnect switchwith a fuse (“feeder with fused disconnect switch”), a lightingcontactor, a resistive contactor or an ATS (automatic transfer switch),by way of further example.

The term “disconnect switch” when used with respect to a unit refers toa switch in or on the unit for controlling energization orde-energization of the unit, including a circuit breaker or a switch foropening and closing separable contacts in, e.g., a circuit breakerand/or for turning power ON and OFF using a switch associated with afuse (e.g., a fused disconnect). A disconnect switch can also include anisolation switch for the bypass unit. The disconnect switch can includean operator mechanism to permit manual operation of the circuit breakeror fused disconnect.

The terms “load” and “load device” are used interchangeably and areintended to mean devices that consume electrical power and that areconnected to and controlled by the electrical power distribution system(e.g., a motor control center). Load devices are typically motors, butmay also be pumps or other machinery that may comprise motors or pumpsor other miscellaneous critical loads such as hospitals, dam emergencypumps, data centers, back-up generator systems and the like.

Referring to FIG. 1, one embodiment of an electrical power distributionsystem 100 (e.g., a MCC) is shown. The electrical power distributionsystem 100 includes a structure with compartments 110, a wire way 100 w(FIG. 4, for example), a common power bus 200, units 50 ₁, 50 ₂ and abypass unit 10 for providing power from the power bus 200 of a power busbar system 1000 (FIG. 4, for example) to an external load 80. Theelectrical power distribution system 100 can include more than two units50 ₁, 50 ₂ and the bypass unit 10 as shown in FIG. 8, for example.

Embodiments of the invention can allow for electrical isolation of oneof the units 50 ₁, 50 ₂, from the other of the units 50 ₁, 50 ₂, whilethe other unit is operational, online, and providing power to the load80, thereby providing a continuous operational system while alsoproviding increased safety for a technician. For example, since theprimary or first unit 50 ₁ is electrically isolated from the secondaryor second unit 50 ₂, a technician can access the first unit 50 ₁ whichis offline and electrically isolated from the second unit 50 ₂, thepower bus 200 (FIGS. 1, 4) and the load 80, while the second unit 50 ₂is operational, online, and providing power to the load 80, therebyproviding a continuous operational system while also providing increasedsafety for a technician.

Embodiments of the invention can also provide for physicalseparation/isolation of the first and second units 50 ₁, 50 ₂ and thebypass unit 10 from each other in compartments 110 of the structure 100using barriers such as partitions, walls, ceilings and floors, forexample.

Referring to FIGS. 1 and 2A, the bypass unit 10 includes a housing 10 hthat encloses a power transfer circuit 20 with a bypass isolation switch25. The power transfer circuit 20 is coupled to a load 80, e.g., a loadside device such as a motor 80 m (FIG. 2A), via a conductor 30, shown asa three pole/three phase lead with three electrical contact connections.The term “conductor” refers to one or more cables, each of which caninclude one or more wires, leads or other elements that conductelectricity, or one or more wires, leads, traces, lines or otherelements that conduct electricity.

The power transfer circuit 20 is also electrically coupled to a firstunit 50 ₁ and a second unit 50 ₂ (FIGS. 1, 3A, 3B, 4-6) via conductors32, 34, respectively, and is configured to only electrically connect theload 80 to a single one unit of the first unit 50 ₁ or the second unit50 ₂ at any one time during normal operation. The conductors 30, 32, 34can be of the same or different lengths. The conductors 32, 34 canextend from the bypass unit 10 to the first and second units 50 _(k), 50₂, inside a wire way 100 w of a structure 100, such as an MCC 100M(FIGS. 4-6).

As shown in FIGS. 2A and 2B, the bypass unit 10 has a front panel 10 f,sidewalls 10 s, a ceiling 10 c, a floor 10 b and a back wall 10 r thatdefines an enclosed compartment 11 and does not require, and typicallydoes not have, power stabs (for engaging a power bus) that extend outfrom the back wall 10 r. A plurality of conductors 30, 32, 34 extend outof the housing 10 h, typically one of the side walls 10 s, shown as theright side wall 10 e (FIG. 2B). The term “right side” refers to theorientation when held in a structure for normal operation with the front10 f facing forward. The incoming conductors (e.g., nine wires, threeassociated with each conductor 30, 32, 34) can be fed into the bypassunit 10 through one side of the unit and into a wire way 100 w (FIG. 4)and the rear 10 r of the housing 10 h can be a closed panel. The bypassunit 10 can electrically isolate each of the first unit 50 ₁ and thesecond unit 50 ₂ from the load 80 and/or from each other whilerespective front panels 50 f (FIGS. 1, 3A, 3B) remain closed andtypically locked in the closed position.

In some embodiments, the housing 10 h of the bypass unit 10 can definean enclosure with a solid back wall 10 r with the conductors 30, 32, 34extending from a common portion or different portions of the housing 10h via a ceiling, floor, sidewall or back wall. The housing 10 h can be a1× size housing (about 6 inches tall) of a 2× size housing (about 12inches tall) in some embodiments.

It is contemplated that embodiments of the invention can comply with therecommendation of IEEE P1814 with respect to a reduced hazardrequirement, which recommends a drive unit, such as a VFD unit, beisolated. Embodiments of the invention can provide a bypass unit thatcouples to both primary and secondary (redundant) units, which cancomprise respective motor starters of the same or different motorstarter types. Embodiments of the invention provide modular buildoptions without requiring expensive, complex and larger cumbersomecustomizations for providing different build configurations whileproviding the bypass power transfer function.

In some embodiments, the technician can interchangeably replace amalfunctioning primary/first unit from the structure 100 of anelectrical power distribution system (FIGS. 1, 3A, 3B) with a modularreplacement unit of the same type (e.g., the same housing and buildconfiguration with the same internal components) while the other(secondary/second) unit is operational.

As shown in FIG. 2B, the bypass unit 10 can include a user interfacemember 130 (which is typically a lever or handle of an operatingmechanism) extending from the front panel 10 f and connected to thepower transfer circuit 20, typically directly coupled to the bypassisolation switch 25. The user interface member 130 can include, e.g., arotary switch, that allows a user to select a first position thatcouples the first unit 50 ₁ to the load 80, a second position thatcouples the second unit 50 ₂ to the load 80, and an optional thirdposition that concurrently disconnects the first unit 50 _(k), thesecond unit 50 ₂ and, optionally, also disconnects the bypass unit 10from the load 80. Thus, there can be first and second “ON” positions andan optional “OFF” position, and, where used, the OFF position can bebetween the first and second ON positions as shown in FIG. 2B.

The user interface member 130 can be a switch handle that is manuallyoperated and configured to receive a lock so as to be able to bephysically locked (e.g., padlocked) in an OFF or ON position. Referringto FIGS. 2A and 2B, the user interface member 130 can have two ONpositions, a first ON position to close a first set 26 ₁ of (three)switch contacts 26 c that couple to the first unit 50 ₁ and the secondON position to close the other set 26 ₂ of (three) switch contacts 26 cthat couple to the second unit 50 ₂ to electrically selectively coupleonly a single one of the units 50 _(k), 50 ₂, The ON position isassociated with the corresponding unit being energized providing anelectrical path from the power bus 1000 (FIG. 4) through the selectivelyclosed switch contacts 26 c of the bypass unit 10 to a load 80 at anyone time.

Still referring to FIG. 2B, the bypass unit 10 can also optionallyinclude a lock 13 that locks the front panel 10 f (which can be a frontdoor that pivots open from a side) closed so that a technician cannotopen the front panel or door 10 f when the lock is deployed. The lock 13can be a physical/mechanical or electromechanical interlock that locksthe front panel or door 10 f closed.

One or all of the units 10, 50 _(k), 50 ₂ (FIGS. 1, 3A, 3B) can beconfigured as a modular unit to allow the internal components to beassembled as a unit 10, 50 _(k), 50 ₂ that can be easily, typicallyslidably and replaceably, installed into a compartment 110 of astructure 100 (FIGS. 1, 3A, 3B) such as an enclosure, a cabinet, and/ora motor control center (MCC) 100M (FIGS. 4-6). Embodiments of theinvention provide modular (plug and play) configurations which canprovide economic advantages to known conventional custom bypass designsthat are cumbersome and may not provide the additional electricalisolation allowed by embodiments of the present invention. To be clear,the term “modular” refers to units that have defined standardizeddimensions so that one unit of one type is replaceably interchangeablewith another unit of that type.

Referring again to FIG. 2A, the bypass unit 10 can be provided inpackage or frame sizes of about 6 inches to about 72 inches (tall) in aheight dimension “H” with substantially common depth and widthdimensions, known as 1× (6 inches) to 12× (72 inches) sizes. The sizescan be in single X increments, from 1×, 2×, 3×, 4×, 5×, 6×, 7×, 8×, 9×,10×, 11× and 12×. Thus, a 5× unit 10 can be about 30 inches tall. Insome embodiments, the bypass unit 10 can be a 1× unit with a height “H”of about 6 inches or a 2× unit with a height H of about 12 inches. Theframe sizes can be provided for target operational amperages, includinga plurality of: 125A, 150A, 225A, 250A, 400A, 600A, 1200A and 2000A, forexample.

FIGS. 1, 3A and 3B illustrate that the bypass unit 10 can be placed in acompartment 110 of a structure 100 and concurrently attached via cables32, 34 but selectively electrically coupled to the first unit 50 ₁ andthe second unit 50 ₂. The first and second units 50 _(k), 50 ₂ can eachbe configured as a motor starter unit comprising a motor starter 50 m(FIGS. 4-6) and a disconnect switch 60 for controlling energization andde-energization of the motor starter 50 m. Each unit 50 _(k), 50 ₂ caninclude a front panel or door 50 f.

The front door 50 f of each unit 50 _(k), 50 ₂ may be configured toengage at least one lock 53 that, when deployed, can lock the door 50 fin the closed position. The lock 53 can be a physical mechanicalinterlock.

In some embodiments, each disconnect switch 60 of the first and secondunits 50 ₁, 50 ₂ includes a circuit breakers 60 b with a shunt trip 60 sas shown schematically in FIG. 7B. The terms “shunt trip” and “shunttrip coil” are used interchangeably herein and are well known componentsof circuit breakers.

The isolation switch 25 of the bypass unit 10 can be configured withopen and closed switch states of each switch contact 26 c (FIG. 2A) sothat only one set 26 _(k), 26 ₂ of three switch contacts/poles 26 c iselectrically active and connected to one of the first and second units50 ₁, 50 ₂ at any one time to provide either a first electrical path P₁between a power bus 200, the first unit 50 _(k), the bypass unit 10, andthe load 80 or a second electrical path P₂ between the power bus 200,the second unit 50 ₂, the bypass unit 10, and the load 80.

Referring to FIGS. 1, 2A, 2B, 3A, 3B, a conductor 502 can be coupled tothe first and second units 50 _(k), 50 ₂ to permit signal communicationtherebetween, to thereby provide electrical interlocking functionality.For example, when a user selects the first unit 50 ₁ to power the loadby switching the user interface member 130 (e.g., operator handle of anoperator mechanism) to an ON position and switching the isolation bypassswitch 25 to Unit 1-ON position, the first unit 50 ₁ (either or both theauxiliary switch of the circuit breaker 60 b or the auxiliary relay 150r of the motor starter 50 m) can transmit a trip signal to the circuitbreaker 60 b of the second unit 50 ₂, typically via the shunt trip 60 s(FIG. 7B). Likewise, the second unit 50 ₂ can transmit a trip signal tothe circuit breaker 60 b of the first unit 50 _(k), typically the shunttrip 60 s (FIG. 7B), when the second unit 50 ₂ is selected by the powertransfer circuit 20 via the isolation bypass switch 25 to create theelectrical path to power the load 80 via the bypass unit 10. This canprovide an extra degree of safety via an electrical interlock system.

Referring to FIGS. 3A, 3B and 7B, the disconnect switch 60 of the firstunit 50 ₁ can electrically couple to the disconnect switch 60 of thesecond unit 50 ₂. In some embodiments, the disconnect switch 60 of eachof the units 50 _(k), 50 ₂ comprises or is a circuit breaker 60 b. Incertain defined conditions, the first unit 50 ₁ can send a trip signalto the circuit breaker 60 of the second unit 50 ₂ to cause the breakershunt trip coil 60 s to trip the breaker in the second unit 50 ₂. Incertain defined conditions, the second unit 50 ₂ can send a trip signalto the circuit breaker 60 b of the first unit 50 ₁ to cause the breakershunt trip coil 60 s to trip the breaker in the first unit 50 _(k).

The first unit 50 _(k), for ease of discussion can be referred to as a“primary unit”, and a second unit 50 ₂, for ease of discussion can bereferred to as a “secondary unit” that can be coupled to the bypass unit10 for selectively powering a load 80 through the power transfer circuitof the bypass unit 10.

In some embodiments, an electrical power distribution system 100 (e.g.,MCC) can include a plurality of different electrical interlocks toensure that only one unit of units 50 ₁, 50 ₂ is energized and capableof providing power to the load 80 through the bypass unit 10 at any onetime. FIG. 11 lists exemplary electrical interlocks. These definedconditions and associated actions can provide an electrical interlocksystem. FIG. 11 lists example actions of the first (primary) unit 50 ₁,the second (redundant) unit 50 ₂, and the bypass unit 10 providing anelectrical interlocking system based on defined operative conditions orstates of the first and second units 50 ₁, 50 ₂.

Example interlocks associated with a primary mode (when the first unit50 ₁ is powering the load 80 through the bypass unit 10) or a bypassmode (when the second unit 50 ₂ is powering the load 80 through thebypass unit 10) are listed. The defined conditions can include positionsof power stabs 554 optionally provided as retractable/extendable powerstabs 546, 548, 550 of a power disconnect assembly 500 (FIGS. 9 and 10)whether the power stabs 546 are fully extended and connected to a powerbus 1000 or retracted (FIGS. 4-6) based on position sensors 582, 594such as one or more microswitches (FIG. 10) in the respective units 50₁, 50 ₂. Other conditions can be based on an energized status of arespective primary or secondary unit based on an auxiliary switch and/orauxiliary relay in each of the first and second units which can send atrip signal to the other unit. The bypass unit 10 can also send a tripsignal to the primary 50 ₁ or secondary unit 50 ₂ depending on whetherthe bypass unit 10 is in the primary mode (trip signal to the secondaryunit) or the bypass mode (trip signal to the primary unit).

However, while the power disconnect assembly 500 is believed to bedesired for certain end applications/uses, it is not required in allmotor starter units. For further description of position sensors usingauxiliary switches such as microswitches in a unit with a powerdisconnect assembly 500, see U.S. 2008/0022673 (labeled as features 82and/or 94 in FIG. 17 of this document), the contents of which are herebyincorporated by reference as if recited in full herein. For furtherdescriptions of example power disconnect assemblies and interlocks, seealso, U.S. patent application Ser. No. 15/848,103, the contents of whichare hereby incorporated by reference as if recited in full herein.

Table 1 below provides a list of example configurations of the firstunit/primary unit 50 ₁ and the second unit/secondary unit 50 ₂.

TABLE 1 UNIT COMBINATION OPTIONS Option Primary Unit Secondary unit AVFD unit VFD unit B Soft Starter Soft Starter (Reduced Voltage starter)unit (Reduced Voltage starter) unit C NEMA Starter unit NEMA Starterunit D IEC Starter unit IEC Starter unit E VFD unit Soft Starter(Reduced Voltage starter) unit F Soft Starter NEMA Starter unit (ReducedVoltage starter) unit G NEMA Starter unit IEC Starter unit H VFD unitNEMA Starter unit I Soft Starter IEC Starter unit (Reduced Voltagestarter) unit J VFD unit IEC Starter unit K Feeder Breaker FeederBreaker L Feeder with Fused Disconnect Feeder with Fused DisconnectSwitch Switch

Referring to FIG. 7B, the trip signal for the electrical interlocksystem can be generated/transmitted via at least one interlock circuit1500 that can include (a) one or more inputs for receiving a signal froman auxiliary switch 27 (FIG. 7A) of the bypass unit 10 via conductor 127and (b) one or more input(s) for receiving a signal from the first andsecond units 50 _(k), 50 ₂ such as from an auxiliary switch or contactassociated with the circuit breaker 60 b of the disconnect switch 60and/or an auxiliary relay 150 r coupled to or in the motor starter 50 m.As discussed above, the first and second units 50 _(k), 50 ₂ can becoupled via a conductor 502, for example. One or more of theoutputs/signals from the auxiliary switch 27 and/or the interlockcircuit 1500 can provide a voltage signal as a trip signal to a shunttrip 60 s in a circuit breaker 60 b of one of the first and second units50 _(k), 50 ₂ when the other unit of the first and second units 50 _(k),50 ₂ has a circuit breaker 60 b that is energized.

Still referring to FIG. 7B, each motor starter 50 m can be coupled to anauxiliary relay 150 r that can transmit a trip signal 150 s to theinterlock circuit 1500. For example, when a motor starter 50 m of one ofthe first and second units first and second units 50 ₁, 50 ₂ is onand/or operating, an auxiliary relay 150 r can transmit a voltage tripsignal 150 s to the circuit breaker 60 b of the other unit to make surethat the other unit is off, contacts open, as a safety interlockfeature.

In some embodiments, the auxiliary relay 150 r of the motor starter(e.g., soft starter) 50 m, the auxiliary switch 27 of the bypass unit 10and an auxiliary switch 60 s in the breaker 60 b of first unit 50 ₁ canbe synchronized and/or transmit in parallel, trip signals to the secondunit 50 ₂ when the first unit 50 ₁ is energized. The auxiliary relay 150r of the motor starter (e.g., soft starter) 50 m, the auxiliary switch27 of the bypass unit 10 and the auxiliary switch 60 s in the breaker 60b of the second unit 50 ₂ can be synchronized and/or transmit inparallel trip signals to the first unit 50 ₁ when the second unit 50 ₂is energized.

The term “auxiliary switch” for the primary unit and the secondary unitin FIG. 11 that can send the trip signal(s) to the appropriate breakercan include one or more auxiliary switches including, for example, anauxiliary switch 582, 594 (FIG. 10) identifying a position of theretractable/extendable power stabs, an auxiliary switch of a circuitbreaker 60 b (FIG. 7B) associated with a contacts closed condition, oran auxiliary relay 150 r (FIG. 7B) of a motor starter 50 m indicating anmotor on condition.

The structure 100 can be designed to slidably receive multiple units 10,50 ₁, 50 ₂ in various defined sizes. For example, the first and secondunits 50 ₁, 50 ₂ can each have housings 50 h of the same or differentmodular heights (i.e., 1×-12× frame sizes as discussed above). Eachhousing 10 h, 50 h can include a front door 10 f, 50 f that can remainclosed when a respective unit is energized. Only one of the two units 50₁, 50 ₂ can be energized when connected to the power bus bars 200 andconnected to the load 80 via the bypass unit 10 at any one time. Whende-energized, one of the front doors 50 f of the two units 50 ₁, 50 ₂can be opened to allow a technician access to replace or repair thatunit while the other of those two units 50 ₁, 50 ₂ is energized butelectrically isolated from the de-energized unit and the bypass unit 10.

FIG. 3A illustrates that the bypass unit 10 can be placed in a firststructure 100 ₁ while the first unit 50 ₁ and the second unit 50 ₂ arein a separate, but typically adjacent, structure 100 ₂. Each structure100 can optionally have a front door 100 f (shown by the shading overthe respective units) that closes and releasably locks via at least onemechanical lock 114 in the closed position over one or more of the units50 _(k), 50 ₂ and 10, respectively.

FIGS. 1 and 3B illustrate that the bypass unit 10 and the first andsecond units 50 ₁, 50 ₂ are held in the same structure 100. FIG. 3Billustrates that the units 50 ₁, 50 ₂ can be held in side by side,laterally adjacent compartments 110. FIG. 1 illustrates that the bypassunit and the first and second units 50 _(k), 50 ₂ can be held in avertically stacked arrangement of compartment 110.

Referring again to FIG. 1, each compartment 110 can have a closed floor110 f and/or ceiling and/or rails 112 coupled to internal sidewalls 1101that slidably receive and support the units 10, 50 _(k), 50 ₂.

Referring to FIGS. 4-6, the first and second units 50 _(k), 50 ₂ canhave power stabs 554 extending rearward from the back 50 r that connectto one or more (typically vertically oriented) power bus bars 200 thatare part of a power bus system 1000 that carries power (current) to thecompartments of a vertical section in the structure such as the MCC100M. These power stabs 554 may optionally be provided by a powerdisconnect assembly 500 as discussed above. As is well known, the busbars 200 can be connected to larger (typically horizontal bus bars) thatbring power to the vertical sections. The larger (typically horizontal)bus bars are usually in the top, but some structures may have them inthe center or bottom. The structures of MCCs 100M usually have at leastone wireway 100 w for conductors 30, 32, 34 (i.e., wires) to the load(s)and control cables and/or wires.

FIG. 4 illustrates an MCC 100M with the bypass unit 10 and a first unit50 ₁ that can comprise a VFD 50 _(VFD) as the motor starter 50 m and canalso comprise power stabs 554, shown as provided by a power disconnectassembly 500. FIG. 4 also illustrates that the second unit 50 ₂ cancomprise a NEMA starter 50 _(Nm) as the motor starter 50 m and can alsocomprise power stabs 554, shown as provided by a power disconnectassembly 500. The microswitches 582 and/or 594 (FIG. 10) can identifywhen the stabs 554 are fully engaged to the (vertical) power bus 200 andwhen the stabs 554 are fully withdrawn and isolated from the (vertical)bus 200.

FIG. 5 illustrates an MCC 100M with the bypass unit 10 and a first unit50 ₁ that can comprise a soft starter 50 ss as the motor starter 50 mand can also comprise power stabs 554, shown as provided by a powerdisconnect assembly 500. FIG. 5 also illustrates that the second unit 50₂ can comprise a NEMA starter 50 _(Nm) as the motor starter 50 m and canalso comprise power stabs 554, shown as provided by a power disconnectassembly 500. The position sensors 582 and/or 594 (FIG. 10) can identifywhen the stabs 554 are fully engaged to the (vertical) power bus 200 andwhen the stabs 554 are fully withdrawn and isolated from the (vertical)power bus 200.

FIG. 6 illustrates an MCC 100M with the bypass unit 10 and a first unit50 ₁ that can comprise a VFD 50 _(VFD) as the motor starter 50 m and canalso comprise power stabs 554, shown as provided by a power disconnectassembly 500. FIG. 6 illustrates that the second unit 50 ₂ can comprisea soft starter 50 ss as the motor starter 50 m and can also comprisepower stabs 554, shown as provided by a power disconnect assembly 500.The position sensors (e.g., microswitches) 582 and/or 594 (FIG. 10) canidentify when the stabs 554 are fully engaged to the (vertical) powerbus 200 and when the stabs 554 are fully withdrawn and isolated from the(vertical) bus 200.

Thus, as shown by the examples of FIGS. 4-6, modular units 50 _(k), 50 ₂of different motor starter configurations can allow a number ofdifferent MCC build selections and/or configurations without requiringunique more expensive custom units.

Referring to FIG. 7A, the bypass isolation switch 25 of the bypass unit10 can comprise a six pole isolation switch with a first set of threepoles 26 ₁ coupled to the first unit 50 ₁ and a second set of threepoles 26 ₂ electrically coupled to the second unit 50 ₂. The switch 25can include a main switch body 25 m with the six poles and one or moreauxiliary switches 27, typically at least one auxiliary switch on eachopposing end or side of the main switch body 25 m.

The auxiliary switches 27 can be configured to receive and/or transmitsignals from and/or to the first unit 50 ₁ and the second unit 50 ₂. Forexample, one or more of the auxiliary switches 27 can transmit a tripsignal to the circuit breaker 60 b of the disconnect switch 60 of one ofthe first unit 50 ₁ or the second unit 50 ₂ either or both (a) when theother of the first unit 50 ₁ or the second unit 50 ₂ is energized withthe stabs 554 contacting the power bus 200 or (b) when the bypass switch25 connects the first or second set of switch contacts 26 c to be in thebypass mode whereby the aux switch 27 sends a trip signal to the primaryunit 50 ₁ or the primary mode whereby the aux switch 27 sends a tripsignal to the secondary unit 50 ₂. A respective auxiliary switch 27 canbe coupled to one or both units 50 _(k), 50 ₂ via a conductive cable 127(e.g., wire(s)) (FIG. 7B).

As also shown in FIG. 7B, the first and second units 50 ₁, 50 ₂ can beelectrically coupled via one or more conductors 502 so that the firstunit 50 ₁ can send a trip signal to the second unit 50 ₂ when the firstunit 50 ₁ is connected to the power bus bars 200. Similarly, the secondunit 50 ₂ can send a trip signal to the first unit 50 ₁ when the secondunit 50 ₂ is connected to the power bus bar 200. In some embodiments,the trip signal can be generated by an auxiliary switch 60 s (FIG. 7B)in a respective unit 50 _(k), 50 ₂ and/or a microswitch assemblyassociated with a position sensor 594 and/or 582 (FIG. 10) associatedwith one of the units with a power disconnect assembly 500 when thestabs of one of the units 50 _(k), 50 ₂ are fully extended and the stabsof the other unit are not extended (i.e., are retracted).

By way of example only and without limitation, an example isolationswitch 25 is an R5 series six pole isolation switch (UL 508) non-fusible16A-80A rotary disconnect that comprises a (rotary) user interfacehandle as the user interface member 130.

FIG. 7B illustrates that the structure 100, optionally an MCC 100M, cancomprise the bypass unit 10 coupled to the first unit 50 ₁ and thesecond unit 50 ₂. Each unit 10, 50 _(k), 50 ₂, can be in separatehousings 10 h, 50 h and placed in separate compartments of the structure100. Each housing 10 h, 50 h can have a closed front panel or door 10 f,50 f.

FIG. 8 illustrates an example MCC 100M with the first and second units50 _(k), 50 ₂ and the bypass unit 10. The first and second units 50_(k), 50 ₂ include operator handles 51 that are coupled to internaldisconnect switches 60, such as circuit breakers, as is well known tothose of skill in the art. The bypass unit 10 includes a user interfacemember 130 (deadfront switch operable through a closed door) which canbe a rotary handle that is coupled to the power transfer circuit 20(FIG. 1) to allow an operator to select to connect power from a load 80to a single one of the first unit 50 ₁ or the second unit 50 ₂ and powerbus 200.

The user interface member 130 can be configured to have three definedpositions for defined ON and OFF states, a primary ON position, aprimary OFF position and a bypass ON position. The user interface member130 can be locked, such as padlocked, in one or both of the bypass ONand primary ON position, and can be interlocked to the door in one orboth of the primary and bypass ON positions, and a door of the unit 10can be locked closed when in an ON position.

Still referring to FIG. 8, a typical MCC structure 100M is an enclosurewith a number of small doors arranged in rows and columns along thefront and flat, mostly featureless, back and sides. The units 10, 50 canbe provided in varying sizes. For starter units 50 ₁, 50 ₂, the size canbe based on the size of the load 80, e.g., motor 80 m (FIG. 2A) they arecontrolling. The units 10, 50 ₁, 50 ₂ can be configured to be relativelyeasily removable for repair, service or replacement. MCCs 100M can havedifferent sets of units, for example, regular starters, reversingstarters, soft start, and variable frequency drives. MCCs 100M can beconfigured so that sections can be added for expansion if needed.

MCCs 100M can be configured in many ways. Each compartment 110 can havea different height to accept different frame sizes of respective bucketassemblies or units 10, typically in about 6-inch increments. Thevertical bus can be omitted or not run through the full height of thesection to accommodate deeper buckets for larger items like variablefrequency drives. The MCC can be a modular cabinet system for poweringand controlling motors and/or feeder circuits. Several may be poweredfrom main switchgear which, in turn, gets its power from a transformerattached to the incoming line from a public or private grid, e.g., apower company.

Referring to FIG. 8, a partial perspective view of a motor controlcenter structure 100M is shown. Units 10, 54, 50 _(k), 50 ₂ are shownfully installed into a motor control center compartment 110 such thatits respective front panel 10 f, 54 f, 50 f is seated securely againstthe periphery of the compartment enclosure and flush with the frontpanel 54 f of unit 54 and with the front panel 50 f of units 50 _(k), 50₂.

In some embodiments, some or all units, e.g., units 54, 55, 50 _(k), 50₂ can include a number of latching mechanisms 22 on front panels thereofso that an operator may lock a unit into place once installed. In someembodiments, the front panel 50 f, 54 f may be a deadfront door having aset of hinges 19 in order to permit access to motor control componentswithin a unit while the unit is installed in a compartment 111 of theMCC 100M. However, even when closed or sealed, front panel or door 50 fstill permits access to the disconnect switch 60 which can comprise acircuit breaker, stab indicator 24, shutter indicator 26, and linecontact actuator 31. Line contact actuator 31 is a mechanism of thepower disconnect assembly 500 (FIG. 9) for selectively engaging a powerbus 200 to engage power stabs 554 defining line contacts (FIG. 4) withline power from the MCC 100M. Thus, even when a unit 10, 50 is fullyinstalled in a compartment 110 and latches 22 have been secured, anoperator may still use respective switch handles 51, 130.

As shown in FIG. 8, the first unit has the handle 51 in an ON positionassociated with conduction and an energized state while the second unit50 ₂ has the handle 51 in an OFF position associated with non-conductionand a de-energized state and the handle 51 can engage a lock 151 such asa padlock to lock the unit 50 ₂ in this state.

For units with the power disconnect assembly 500, a user can also openslide 132 to insert crank 134 to move one or more line contacts (notshown) of the unit. When slide 132 is moved laterally aside to permitaccess to actuating mechanism 131, door 50 f is prevented from opening,thereby closing off access to components inside the unit 50 _(k), 50 ₂.Additionally, a user may desire to padlock 232 the slide 132 in theclosed position (FIG. 14B), to further regulate who may operateactuating mechanism 131 and when.

When slide 132 is moved aside, an aperture 136 (FIG. 9) is exposed.Opening 36 accepts a crank 134. Additionally, when slide 132 is movedaside as shown, slide 132 may optionally extend over a portion of frontpanel 50 f. Thus, in embodiments in which front panel 50 f is a hingeddoor, moving slide 132 to expose aperture 136 will inhibit a user fromopening front panel 50 f. Accordingly, so long as an operator has acrank 134 inserted into aperture 136 aligned with the internal actuator131, the operator cannot open the door of the unit 50 _(k), 50 ₂.

FIGS. 9 and 10 show an example unit 50 _(k), 50 ₂ with an operatorhandle 51 coupled to the disconnect switch 60 and a power disconnectassembly 500 with retractable/extendable power stabs 554. During theextension of the power disconnect assembly 500 with the stabs 554 anautomatic latch 60 can be triggered to engage the compartment 110 intowhich unit 50 _(k), 50 ₂ has been installed. Also due to the extensionof the power disconnect assembly 500, a rod 78 is pulled by a stabbracket 59 such that a cam 80 is rotated away from a microswitch 582.Microswitch 582 is thus actuated to permit control voltage from acontrol power contact 44 to a motor control component, such as acontactor or overload relay (not shown). It is appreciated, however,that the position sensor assembly using the microswitch 582, cam 80 androd 78 can be provided in other manners.

Also shown in FIG. 10 a second microswitch 594 can be connected toactivate and deactivate a disconnect switch 60 such as a circuitbreaker. When stabs 546, 548, 550 reach the fully engaged position withbus bars 200, stab bracket 59 actuates microswitch 594. When actuated,microswitch 594 permits closure of the disconnect switch 60, completingthe circuit between bus bars 200 and the line side of motor controlcomponents (not shown) in unit 50 _(k), 50 ₂. Otherwise, microswitch 594can prevent closure of its disconnect switch 60, e.g., circuit breaker.The microswitch 594 of the first unit 51 can send a trip signal to thedisconnect switch 60 of the second unit 50 ₂ when the microswitch 594permits closure of its disconnect switch to trip the disconnect switch60 in the second unit 50 ₂ (and vice versa). This can be the signaltransmitted via conductor 502 (FIGS. 3A, 3B, 3C, 7B).

Control power stab 44 can be un-shielded and connected to a controlpower once a respective unit 50 ₁, 50 ₂ is installed into a motorcontrol center. However, microswitch 582 is in an activated state, dueto the pressure thereon by cam 80. When microswitch 582 is in theactivated state, as shown, microswitch 582 is interrupting control powerfrom contact 44. Thus, the motor control components (not shown) housedin the unit housing 50 h cannot initially be operated. Cam 80 will bemoved by rod 78 via advancement of stab bracket 59, deactivatingmicroswitch 582 and thereby permitting the flow of control power tomotor control components (not shown) of the unit. Cam 80 also acts todisplay a location status of the stabs 546, 548, 550 to an operator. Cam80 can have a number of colors thereon which can be displayed throughfront door 50 f of the unit via stab indicator 24 (FIG. 8).

In the embodiment shown in FIG. 10, a disconnect switch (e.g., circuitbreaker) interlock 316 includes microswitch 594, which gates theoperation of the disconnect switch 60. FIG. 10 shows microswitch 594 ina deactivated state, in which button 334 thereof is not depressed. Arm330 of microswitch 594 is positioned to abut a ledge 332 of interlock316. Thus, when disconnect switch interlock 316 moves, due to the motionof stab assembly 58, the arm 330 of microswitch 594 will pivot,depressing button 334. When button 334 is depressed, microswitch 594will be activated and will electrically allow operation of thedisconnect switch (FIGS. 4-6).

FIG. 9 also has height “H”, width “W” and depth “D” dimensions which maybe provided in modular frame sizes of 1×-12× as discussed above withrespect to the bypass unit 10. In some embodiments, the bypass unit 10has a height that is less than the height of the units 50 _(k), 50 ₂.The bypass unit 10 and the units 50 _(k), 50 ₂ can have common depth andwidth dimensions. In other embodiments, the units 50 _(k), 50 ₂ can havecommon depth and width dimensions and the bypass unit 10 can have adifferent depth and/or width dimension.

Also shown in FIG. 10 is a shutter arm 336, having a sloped end 338. Asstab 546 is advanced, stab 546 will engage the sloped end 338 and slidepast shutter arm 336, thereby shifting shutter arm 336 to the left, asdepicted in FIG. 10. When shutter arm 336 is shifted, it will strike atab 340 of a rod 76 extending in a front to back direction of the unit.When tab 340 is struck, rod 76 will rotate, changing the color showingon shutter indicator 26 through door 50 f of a respective unit 50 _(k),50 ₂.

The electrical power distribution systems 100 (e.g., MCCs) contemplatedby embodiments of the invention can optionally include one or moremechanical interlocks. FIG. 12 lists example mechanical locks that canoptionally be used to provide a mechanical interlocking system to ensurethat only one unit of units 50 _(k), 50 ₂, is energized and capable ofproviding power to the load through the bypass unit 10 at any one time.

The user interface member 130 of the bypass unit 10 providing a lever ofa unit operating mechanism can be padlocked or otherwise locked into aprimary mode when powering the load through the first unit 50 ₁ or thebypass mode when powering the load through the second unit 50 ₂.

For embodiments where units 50 _(k), 50 ₂ comprise the optional powerdisconnect assembly 500 (FIGS. 4-6, 9, 10), when one unit is energized,the other unit can be padlocked via padlock 132 (FIG. 14B) or a padlockthat locks the operator mechanism 130 to lock the unit that is not beingused to power the load to lock the power disconnect assembly 500 withits stabs in a retracted state with the slide 32 (FIGS. 8, 9) misalignedfrom portal 36 and can also padlock the operator mechanism 130 in theoff/open contacts position.

A third interlock may be used where a trapped-key interlock device 250of a unit 50 _(k), 50 ₂ that allows a disconnect switch 51 (e.g.,breaker) to be operated only when the key is turned to allow the handle51 to be turned to the ON position (FIGS. 13A, 13B, 14A). As is known tothose of skill in the art, a trapped-key interlock typically has a lockcylinder which operates a sliding bolt through a cam. The sliding bolt,when extended, mechanically prevents operation of a switch, valve, gate,or other device. Many variations exist, with different shapes ofinterlock bolt and multiple lock cylinders on an interlock. The key isheld or trapped in one position of the lock; releasing the key indicatesthat the interlocked device has been made safe; the interlocked devicecannot be re-energized until the key has been returned and operated toretract the bolt. An example of a trapped-key interlock device 250 is aKirk® key safety interlock from Kirk Key Interlock Company, NorthCanton, Ohio.

A first standard unit 50 ₁ with a first motor starter (e.g., a VFD, Softstarter, NEMA starter, IEC starter or the like) can be referred to asunit “A” and a second standard unit 50 ₂ as a redundant unit with amotor starter of the same or different type (e.g., a VFD, Soft starter,NEMA starter or IEC starter of the like) can be referred to as unit “B”and can be placed in an adjacent location next to unit A. A third(compact) unit “C” provided as the bypass unit 10 comprises the powertransfer circuit 20 with a transfer switch 25 which controls theconnection to the load 80, and which switches motor control from theunit “A” to unit “B”. Both unit A and unit B can comprise powerdisconnect assemblies 500 allowing for (FlashGard™ isolator featuresproviding arc flash safety, e.g., a stab racking mechanism with busisolation and stab position indicators) power bus isolated unitconfigurations. The disconnect switches 60 in the two units can beconfigured as main circuit breakers that can be mechanically interlockedwith a mechanical lock such as a Kirk® Key interlock and can also beelectrically interlocked with shunts trip accessories controlled byposition sensors such as microswitches and auxiliary switches in thoseunits 50 _(k), 50 ₂ associated with, for example, FlashGard™ isolatorsand interlocks. As each unit 50 _(k), 50 ₂ has a separate unit door 50f, each of these units can be electrically isolated and completelydisconnected from the power bus 200, i.e., a 480V/600V system, providinga safe working environment.

The unit 10, 50 _(k), 50 ₂ can be configured for DC (direct current)and/or AC (alternating current) operation.

In some embodiments, the disconnect switch 60 of the unit 50 cancomprise a molded case circuit breaker. Molded case circuit breakers arewell known to those of skill in the art, as exemplified by U.S. Pat.Nos. 4,503,408 and 5,910,760, the contents of which are incorporatedherein by reference as if recited in full herein. In other embodiments,the disconnect switch 60 can comprise a fused disconnect switch to turnpower on and off. Either rotary or up/down operator mechanism switchhandles can be used.

Exemplary fuses are FUSETRON™ 600V Class RK5 fuses (BU-SB13729)available from Cooper Bussmann Company, St. Louis, Mo. However, thedesign is flexible and can accommodate other fuses including those indifferent classes.

FIGS. 15A and 15B illustrate example actions that can be carried outaccording to embodiments of the present invention.

A bypass unit with a power transfer circuit is the power transfercircuit is provided. The power transfer circuit is electrically coupledto only two units and is configured to serially electrically couple oneof the two units to a load, each of the two units having a motor starterand respective disconnect switch (block 800).

Power from a power bus is selectively provided to a load through thepower transfer circuit and only one of the first unit or the second unitat any one time to thereby allow power transfer from a first unit to asecond while electrically isolating the first unit from the load and thesecond unit (block 810).

When the first unit is powering the motor and has a failure, the firstdisconnect switch is turned off to prevent electrical conduction in thefirst unit (block 820).

The first disconnect switch is locked in the off position (block 830).

The second disconnect switch is turned on to allow electrical conductionin the second unit. Power from the power bus, through the second unitand the power transfer circuit is provided to the load (block 840).

A user is allowed to slidably withdraw or otherwise access the firstunit while the second unit is operative (electrically active), with thefirst unit electrically isolated from the bypass unit and the secondunit to thereby allow safe repair, servicing or replacement of the firstunit while powering the load through the second unit and providingelectrical isolation from the power transfer circuit in the bypass unitand the second unit (block 850).

The power transfer circuit can include a six pole isolation switch, withone set of three of the six poles (switch contacts) coupled to the firstunit and another set of three of the six poles (switch contacts) coupledto the second unit. The isolation switch is configured with open andclose switch states of each pole (switch contact) so that only one setof three poles is electrically active and connected to one unit at anyone time to serially provide a first electrical path between the powerbus, the bypass unit, and the load and a second electrical path betweenthe power bus, the bypass unit, and the load (block 802)

The bypass unit with the power transfer switch cooperates with the firstand second disconnect switches to force a shunt trip coil to trip thefirst disconnect switch (primary breaker) in the first unit to off(e.g., opens the primary breaker) (block 804).

The bypass unit and the first and second units have a common width andmodular housings and are slidably mountable in compartments of astructure of an MCC, each unit with respective front doors that can beindependently locked (block 808).

The bypass unit is in an enclosed housing having a rear wall and first,second and third conductors that extend out of the bypass unit, thefirst conductor (only) coupled to the first unit and the secondconductor (only) coupled to the second unit to electrically couple thefirst and second units to the load via the bypass unit (block 806).

Extending retractable/extendable power stabs of a power disconnectassembly of the first unit to electrically engage the power bus while afront door of the first unit remains closed (block 812).

The first and second units comprise electrical and mechanical interlocksconfigured to allow only one of the first and second disconnect switches(e.g., circuit breakers) to be ON at any one time (block 814).

Retracting the retractable/extendable power stabs to disengage from thepower bus while a front door of the first unit remains closed (block822).

The bypass unit can have an external user switch input that accepts userinput to close one of the first set or the second set of switch contactsof a six pole isolation switch. When transferring power from the firstunit to the second unit, the first set of switch contacts are opened andthe second set of switch contacts are closed (block 824).

The method can include extending retractable/extendable power stabs of apower disconnect assembly of the second unit to electrically engage thepower bus while a front door of the second unit remains closed (block842).

FIG. 16 is a flow chart of an example modular assembly method, allowingfor standardized builds from defined sets of different units avoidingunique single build customization according to embodiments of thepresent invention.

A bypass unit is provided. The bypass unit comprising a power transferswitch configured to electrically couple to two units with respectivemotor starters to serially power a load and thereby provide a redundant,back-up drive capacity (block 900). Two units are selected to connect tothe bypass unit from at least three different modular units, optionallytwo of the same or two different ones from the following at least threetypes (block 910).

A first unit can comprise a variable frequency drive (block 912). Asecond unit can comprise a NEMA starter (block 914), and a third unitcan comprise a soft starter (block 916).

The first, second and third units can each comprise a power disconnectassembly having extendable/retractable power stabs (block 920).

The bypass unit and the selected two units can be slidably inserted intocompartments of a structure, such as a structure of an MCC and the powertransfer switch of the bypass unit is electrically coupled to theselected two units during, before or after the inserting (block 925).

It is contemplated that both “new” builds and field-retrofit structuresof electrical power distribution systems 100, such as MCCs 100M, canbenefit from the new bypass unit 10 and primary and secondary units 50₁, 50 ₂ discussed above.

The foregoing is illustrative of the present invention and is not to beconstrued as limiting thereof. Although a few exemplary embodiments ofthis invention have been described, those skilled in the art willreadily appreciate that many modifications are possible in the exemplaryembodiments without materially departing from the novel teachings andadvantages of this invention. Accordingly, all such modifications areintended to be included within the scope of this invention. Therefore,it is to be understood that the foregoing is illustrative of the presentinvention and is not to be construed as limited to the specificembodiments disclosed, and that modifications to the disclosedembodiments, as well as other embodiments, are intended to be includedwithin the scope of the invention.

That which is claimed is:
 1. An electrical power distribution systemcomprising: a power bus; a bypass unit comprising a power transferswitch coupled to a load; a first unit comprising a first disconnectswitch configured to couple the power bus to the power transfer switch;and a second unit comprising a second disconnect switch configured tocouple the power bus to the power transfer switch, wherein the powertransfer switch of the bypass unit is configured to selectively couplethe first unit to the load or the second unit to the load, wherein, whenthe first disconnect switch is closed and the power transfer switchcouples the first unit to the load, the second disconnect switch is opento electrically isolate the second unit from the load and the firstunit, and wherein, when the second disconnect switch is closed and thepower transfer switch couples the second unit to the load, the firstdisconnect switch is open to electrically isolate the first unit fromthe load and the second unit, wherein the first and second units eachfurther comprise a respective housing and a respective power disconnectassembly with extendable/retractable power stabs that independently moverelative to the respective housing to connect to and disconnect from thepower bus, and wherein the extendable/retractable power stabs of onlyone of the first unit or the second unit is permitted to be connected tothe power bus at any one time.
 2. An electrical power distributionsystem comprising: a power bus; a bypass unit comprising a powertransfer switch coupled to a load; a first unit comprising a firstdisconnect switch configured to couple the power bus to the powertransfer switch; and a second unit comprising a second disconnect switchconfigured to couple the power bus to the power transfer switch, whereinthe power transfer switch of the bypass unit is configured toselectively couple the first unit to the load or the second unit to theload, wherein, when the first disconnect switch is closed and the powertransfer switch couples the first unit to the load, the seconddisconnect switch is open to electrically isolate the second unit fromthe load and the first unit, and wherein, when the second disconnectswitch is closed and the power transfer switch couples the second unitto the load, the first disconnect switch is open to electrically isolatethe first unit from the load and the second unit, wherein the bypassunit comprises a housing with a front wall, side walls and a closed rearwall and is devoid of power stabs, wherein the bypass unit connects tothe power bus only through the first unit or the second unit whereby thebypass unit does not directly connect to the power bus, and wherein thefirst unit and the second unit electrically connect to the load onlythrough the power transfer switch of the bypass unit.
 3. An electricalpower distribution system comprising: a power bus; a bypass unitcomprising a power transfer switch coupled to a load; a first unitcomprising a first disconnect switch configured to couple the power busto the power transfer switch; and a second unit comprising a seconddisconnect switch configured to couple the power bus to the powertransfer switch, wherein the power transfer switch of the bypass unit isconfigured to selectively couple the first unit to the load or thesecond unit to the load, wherein, when the first disconnect switch isclosed and the power transfer switch couples the first unit to the load,the second disconnect switch is open to electrically isolate the secondunit from the load and the first unit, and wherein, when the seconddisconnect switch is closed and the power transfer switch couples thesecond unit to the load, the first disconnect switch is open toelectrically isolate the first unit from the load and the second unit,wherein each of the bypass unit, the first unit and the second unitinclude a separate housing that is independently insertable andremovable from a respective compartment in at least one structure of theelectrical power distribution system, and wherein adjacent compartmentsare separated from each other by at least one wall to physically isolaterespective adjacent units from each other.
 4. The electrical powerdistribution system of claim 1, further comprising at least onestructure with defined spaced-apart internal compartments that hold thebypass unit, the first unit and the second unit in different ones of thedefined spaced-apart internal compartments, wherein the first unit andthe second unit are separately and slidably removable from the internalcompartments, wherein the first unit comprises a first front door with afirst disconnect operator handle operably coupled to the firstdisconnect switch, wherein the second unit comprises a second front doorwith a second disconnect operator handle operably coupled to the seconddisconnect switch, and wherein the electrical power distribution systemcomprises interlocks that (a) prevent the first front door from openingwhen either the first disconnect switch is closed or the first unit iscoupled to the load and (b) prevent the second front door from openingwhen either the second disconnect switch is closed or the second unit iscoupled to the load.
 5. The electrical power distribution system ofclaim 1, wherein the bypass unit and the first and second units are eachconfigured to be insertable into and removable from spaced-apartcompartments of a structure, and wherein the bypass unit and the firstand second units each include an operator mechanism coupled to arespective user-accessible operator handle that is configured to bepadlocked in an ON and OFF position.
 6. The electrical powerdistribution system of claim 1, wherein the first disconnect switchincludes a first circuit breaker and the second disconnect switchincludes a second circuit breaker, and wherein the first and secondcircuit breakers are electrically interlocked, such that only one of thefirst and second circuit breakers can be closed at any one time, whereinthe first and second units are operatively connected and configured tocause a first one of either the first circuit breaker or the secondcircuit breaker to trip to an open state when a second one of the firstcircuit breaker or the second circuit breaker is closed to allow only asingle one of the first or second circuit breaker to be in an on stateat any one time.
 7. The electrical power distribution system of claim 1,wherein the electrical power distribution system is a motor controlcenter (MCC), and wherein the first and second units comprise motorstarters.
 8. The electrical power distribution system of claim 1,wherein the first disconnect switch includes a first circuit breaker andthe second disconnect switch includes a second circuit breaker, andwherein the first and second circuit breakers and the power transferswitch are electrically interlocked, such that, when the power transferswitch couples one of the first and second units to the load, only theassociated first or second circuit breaker can be closed.
 9. Theelectrical power distribution system of claim 8, wherein the powertransfer switch further comprises at least one auxiliary switch coupledto the first and second circuit breakers that is configured to transmita trip signal to the first circuit breaker of the first disconnectswitch when the power transfer switch couples the second unit to theload.
 10. An electrical power distribution system comprising: a powerbus; a bypass unit comprising a power transfer switch coupled to a load;a first unit comprising a first disconnect switch configured to couplethe power bus to the power transfer switch; and a second unit comprisinga second disconnect switch configured to couple the power bus to thepower transfer switch, wherein the power transfer switch of the bypassunit is configured to selectively couple the first unit to the load orthe second unit to the load, wherein, when the first disconnect switchis closed and the power transfer switch couples the first unit to theload, the second disconnect switch is open to electrically isolate thesecond unit from the load and the first unit, and wherein, when thesecond disconnect switch is closed and the power transfer switch couplesthe second unit to the load, the first disconnect switch is open toelectrically isolate the first unit from the load and the second unit,wherein the first unit comprises a first motor starter and the secondunit comprises a second motor starter, wherein the first unit isprovided in a first housing enclosing the first disconnect switch andcomprising a first power stab assembly with power stabs that areretractable and extendable relative to the first housing and the secondunit is provided in a second housing enclosing the second disconnectswitch and comprising a second power stab assembly with power stabs thatare retractable and extendable relative to the second housing.
 11. Theelectrical power distribution system of claim 1, wherein the first unitand the second unit comprise motor starters configured as one of optionsA-L: Option first unit second unit A VFD unit VFD unit B Soft StarterSoft Starter (Reduced Voltage starter) unit (Reduced Voltage starter)unit C NEMA Starter unit NEMA Starter unit D IEC Starter unit IECStarter unit E VFD unit Soft Starter (Reduced Voltage starter) unit FSoft Starter NEMA Starter unit (Reduced Voltage starter) unit G NEMAStarter unit IEC Starter unit H VFD unit NEMA Starter unit I SoftStarter IEC Starter unit (Reduced Voltage starter) unit J VFD unit IECStarter unit K Feeder Breaker Feeder Breaker L Feeder with FusedDisconnect Feeder with Fused Disconnect Switch Switch.


12. An electrical power distribution system comprising: a power bus; abypass unit comprising a power transfer switch coupled to a load; afirst unit comprising a first disconnect switch configured to couple thepower bus to the power transfer switch; and a second unit comprising asecond disconnect switch configured to couple the power bus to the powertransfer switch, wherein the power transfer switch of the bypass unit isconfigured to selectively couple the first unit to the load or thesecond unit to the load, wherein, when the first disconnect switch isclosed and the power transfer switch couples the first unit to the load,the second disconnect switch is open to electrically isolate the secondunit from the load and the first unit, and wherein, when the seconddisconnect switch is closed and the power transfer switch couples thesecond unit to the load, the first disconnect switch is open toelectrically isolate the first unit from the load and the second unit,wherein the power transfer switch comprises a six-pole isolating switch,wherein the six-pole isolating switch comprises a first set of threeswitch contacts coupled to the first unit and a second set of threeswitch contacts coupled to the second unit to thereby allow the six-poleisolating switch to selectively couple the first unit or the second unitto the load.
 13. The electrical power distribution system of claim 12,wherein the bypass unit further comprises a first conductor coupled tothe first set of switch contacts, a second conductor coupled to thesecond set of switch contacts, and a third conductor configured tocouple to the load, the first conductor extending from the bypass unit adistance sufficient to couple to the first unit, the second conductorextending from the bypass unit a distance sufficient to couple to thesecond unit, and the third conductor having a length sufficient tocouple to the load.
 14. The electrical power distribution system ofclaim 13, wherein the first and second conductors extend from the bypassunit through a wire way to connect to the respective first and secondunits.
 15. The electrical power distribution system of claim 1, whereinthe electrical power distribution system is a motor control center(MCC), wherein the first unit and the second unit each comprise a lockthat, when deployed, physically (a) locks the power disconnect assemblyin at least one defined position associated with one or both (i) aretracted position associated with an electrically isolated state of therespective unit or (ii) an extended position associated with engagementwith the power bus and an electrically active state, and/or (b) locks alaterally movable slide from allowing access to an aperture that allowsa crank to change a position of the power stabs.
 16. The electricalpower distribution system of claim 15, further comprising at least oneinterlock that is configured to allow a user to open or slidably removeone of the first unit or the second unit from the MCC only when arespective unit is in the electrically isolated state while allowinganother one of the first unit or the second unit to be energized andpower the load through the bypass unit.
 17. The electrical powerdistribution system of claim 1, wherein each of the first and secondunits is devoid of wheels and is slidably and releasably held in definedseparate compartments of a structure of the electrical powerdistribution system and each is serially interchangeable with adifferent corresponding unit having a common size and shape housingthereby allowing modular repair and replacement, and wherein the bypassunit is held in a housing with a closed front door and has a height thatis in a range of about 6-12 inches.
 18. An electrical power distributionsystem comprising: a power bus; a bypass unit comprising a powertransfer switch coupled to a load; a first unit comprising a firstdisconnect switch configured to couple the power bus to the powertransfer switch; and a second unit comprising a second disconnect switchconfigured to couple the power bus to the power transfer switch, whereinthe power transfer switch of the bypass unit is configured toselectively couple the first unit to the load or the second unit to theload, wherein, when the first disconnect switch is closed and the powertransfer switch couples the first unit to the load, the seconddisconnect switch is open to electrically isolate the second unit fromthe load and the first unit, and wherein, when the second disconnectswitch is closed and the power transfer switch couples the second unitto the load, the first disconnect switch is open to electrically isolatethe first unit from the load and the second unit, wherein the bypassunit, the first unit and the second unit are held in separate housings,wherein the bypass unit, the first unit and the second unit areconfigured to power a load with horsepower in a range of about ¼horsepower to 200 horsepower, and wherein the bypass unit has a closedfront door with a front operating switch handle coupled to an isolationswitch of the power transfer switch.
 19. An electrical powerdistribution system comprising: a power bus; a bypass unit comprising apower transfer switch coupled to a load; a first unit comprising a firstdisconnect switch configured to couple the power bus to the powertransfer switch; and a second unit comprising a second disconnect switchconfigured to couple the power bus to the power transfer switch, whereinthe power transfer switch of the bypass unit is configured toselectively couple the first unit to the load or the second unit to theload, wherein, when the first disconnect switch is closed and the powertransfer switch couples the first unit to the load, the seconddisconnect switch is open to electrically isolate the second unit fromthe load and the first unit, and wherein, when the second disconnectswitch is closed and the power transfer switch couples the second unitto the load, the first disconnect switch is open to electrically isolatethe first unit from the load and the second unit, wherein the powertransfer switch of the bypass unit comprises a six-pole isolation switchdefining a main switch body and at least one auxiliary switch attachedthereto, and wherein the at least one auxiliary switch is configured totransmit and/or receive control signals to/from at least one of thefirst or second units.
 20. The electrical power distribution system ofclaim 14, wherein the first and second conductors extend out from aright side of the bypass unit.